This invention relates to a voltage drop warning apparatus with negative-resistance device which warns that a voltage drop has occurred or is occurring. More particularly, this invention concerns a voltage drop indicator which is capable of indicating that a voltage drop has once occurred or is now occurring, through an indication by a light-emitting diode, etc.
In electronic digital clocks or electric clocks operating with an A.C. electric power source supply, by means of synchronization with the frequency of the A.C. power source the time measurement is very accurate. However, in such electronic or electric clocks operating with the A.C. power source, once the power supply is interrupted or disturbed, the time lags behind forever even after restoration from the interruption or disturbance, and moreover, the user usually does not become aware of the time lag.
In electronic digital clocks or electric clocks operating with a D.C. power source as, for instance, a dry cell, when the power source becomes weak and lowers its output power below a specified threshold level, the time becomes inaccurate. In order to check such weakening of the power source, any known voltage indication devices such as a light-emitting diode, miniature incandescent lamp or ammeter can be used, but power consumption of such a device should be made very low. One proposed device comprises a push-button switch which is closed by pressing for the voltage checking, but such device has a drawback that the indication of lowering voltage is obtainable only when the button is pressed.